1H-Pyrazolo[5,1-c]-1,2,4-triazole compounds are useful compounds as magenta couplers for use in developing silver halide color films. Several methods of synthesizing compounds of this class are known. However, these known methods have various disadvantages.
One known method for synthesising 1H-pyrazolo[5,1,-c]-1,2,4-triazole compounds is described in U.S. Pat. No. 3,725,067, U.K. Patent No. 1,252,418 and in the "Journal of the Chemical Society", Perkin I,pp. 2047-2052 (1977). According to this method, a 5-hydrazino-1H-pyrazol-4-carboxylate compound is acylated to obtain a 5-acylhydrazino-1H-pyrazol-4-carboxylate compound, and then the resulting acylated compound is heated under reflux with benzene and phosphorous oxychloride for a relatively long time to thereby obtain a 1H-pyrazolo[5,1-c]-1,2,4-triazole compound.
However, the above-mentioned known method has the following disadvantages. That is, two steps are required in this method to obtain the intended compound from a 5-hydrazino-1H-pyrazol-4-carboxylate compound. Moreover, much time should be allowed to complete the ring closure reaction. Further, when the intended 1H-pyrazolo[5,1-c]-1,2,4-triazole compound has a substituent group reactive to phosphorous oxychloride, such as for example a carboxyl group or a hydroxyl group, the yield of the intended compound is considerably lowered. Furthermore, phosphorous compounds formed as a result of this reaction should be treated in order to avoid environmental pollution, and this treatment may be a heavy burden when commercially practicing the above method.
Another known method of preparing 1H-pyrazolo[5,1c]-1,2,4-triazole compounds is disclosed in JP-A-62-158283 (the term "JP-A" as used herein means an unexamined published Japanese Patent Application). This method comprises acylating a 5-hydrazino-1H-pyrazole compound to obtain a 5-acylhydrazino-1H-pyrazole compound, subsequently reacting the 5-acylhydrazino-1H-pyrazole compound with thionyl chloride, and then ring-closing the resulting compound in the presence of an alcohol to thereby obtain a 1H-pyrazolo[5,1-c]-1,2,4-triazole compound.
However, this method has similar disadvantages to those of the aforementioned method. For example, several steps are required for the reaction of this method, and when the intended 1H-pyrazolo[5,1,-c]-1,2,4-triazole compound has a substituent group reactive to thionyl chloride, such as for example a carboxyl group or a hydroxyl group, the yield of the intended compound is considerably lowered. Further, sulfur dioxide from this reaction needs to be treated so as to prevent environmental pollution, and this is a heavy burden when this method is commercially practiced.
Accordingly, it is an object of the present invention to provide a process for preparing 1H-pyrazolo[5,1-c]-1,2,4-triazole compounds from 5-hydrazino-1H-pyrazole compounds by a one-step reaction which is completed in a short time with high yields.
It is another object of the present invention to provide a process for preparing 1H-pyrazolo[5,1-c]-1,2,4-triazole compounds in high yields even when a substituent group reactive to phosphorous oxychloride, thionyl chloride or the like is present in the molecules of said compounds.
It is a further object of the present invention to provide a process for preparing 1H-pyrazolo[5,1-c]-1,2,4-triazole compounds without the formation of phosphorous compounds and sulfur dioxide, which are harmful substances from an environmental viewpoint.